Fix cpan #79814: Install to 'site' for perl 5.11+

Thanks to Robert Sedlacek for providing a patch.
Fix cpan #80314: make use of PERL_NO_GET_CONTEXT the default
Fix cpan #81484: fix isASCII and isCNTRL for inputs > 255

Thanks to Karl Williamson for providing a patch.
Fix cpan #81796: my $_ is deprecated

Thanks to Nicholas Clark for providing a patch.
Fix cpan #86975: Deterministically order API elements in POD

Thanks to Karl Williamson for providing a patch.
Fix cpan #87870: Merge core perl commit 90b0dc0e2e

Thanks to Father Chrysostomos for the original patch and to Steve Hay
for forwarding it.
Adapt buildperl.pl for newer Perl releases
Update copyright
Update HACKERS
Fix PL_signals code for PERL_NO_GET_CONTEXT
Minor tweaks to devel/ and MANIFEST.SKIP
API update
Add dummy PPPort.xs
Release Devel-PPPort-3.21